Corrected airflow question

[Z24O]

Hi guys/gals,

 

i am attempting to unravel the mysteries of compressor maps

 

i understand the pressure ratio column(14.7 psi/BAR boost adding to 1 Bar atmospheric pressure)

i understand the surge line(you don't want any of the engines operating range to go outside of it)

i understand you want to keep within the best % efficiency throughout the rev range(not sure what the lower limits of efficiency are acceptable)

 

BUT how do you workout the lbs/min for a given engine at a particular revs??

cheers,paul

australia

disclaimer: "i understand" interchangeable with "i think i understand"

[thehelix112]

This must've been covered about a zillion times elsewhere on the net.

 

Maybe start by reading the garrett tech info.

 

http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech103.html

[Z24O]

thanks helix,

finished turbo school ala garrett.....interesting and informative,did my figures and looked at some maps

 

what puzzles me is i was trying to plot RPM/airflow/MAP but all my calculations from 11 lbs/min(1500rpm) to 41 lbs/min(5500rpm) showed very little difference in MAP(around 35psi)....am i doing something wrong?i expected MAP to rise with airflow,not stay reasonably constant.

 

also when you plot a point on the compressor map ,ideally where should it be relative to the efficiency islands for a streetable car(low rev torque)

 

what i am really trying to work out is for an RB30sohc what does the torque/boost/rpm curve look like for a GT30R and GT35R with either .63 or .82 turbine housings....anyone got one?

thanks

paul

[Z24O]

....you around helix??

[thehelix112]

Errr.. I don't know if I'm understanding the question mate.

 

You pick what hp/boost you think your engine can run, pick the approximate rpm the engine will make this boost, plot that point, plot idle air flow point at PR of 1, then draw a line from the second point to the 1st point, then a horizontal line from the first point across to max RPM.

 

This will tell you what efficiency the compressor is working at throughout its working range.

 

Dave